The present invention relates generally to backfill for bridge abutments. More particularly, the present invention relates to using lightweight foam as a bridge abutment backfill to provide support for a pavement surface adjacent to a bridge.
The use of conventional concrete and steel abutments in the construction of bridges is known in the art. Bridge abutments typically have a front side and a rear side. The front side is oriented towards the bridge and the rear side is oriented towards a pavement structure that is adjacent to the bridge. Traditionally, bridge abutments are designed to withstand vertical forces from the bridge and horizontal forces from conventional earthen fill beneath the adjacent pavement structure.
In constructing the bridge, it is desirable for the height of the pavement structure to be at approximately the same as the height of the bridge so as to provide a smooth transition when traveling from the pavement structure to the bridge and vice versa. It is also desirable to construct the bridge so that the pavement structure and the bridge remain at approximately the same height when the pavement structure and the bridge are subjected to forces resulting from vehicles traveling over the pavement structure and the bridge.
When the pavement structure and the bridge are not at the same height, vehicles experience a bump when traveling from the pavement structure to the bridge and vice versa. The bump is undesirable because it applies additional forces to the pavement structure and the bridge and because it can be annoying to vehicle drivers. These forces result in a more rapid deterioration rate for the pavement structure and the bridge than would conventionally be expected.
The difference in height between the pavement structure and the bridge typically occurs when the earthen fill beneath the pavement structure settles at a different rate than the abutment. Thus, it is desirable to prevent the earthen fill on the rear side of the abutment from settling.
Adsorption of water into conventional earthen fill material also causes problems when the water freezes and melts. The freezing and melting of the water in the earthen fill causes the earthen fill to expand and contract. As the earthen fill expands and contracts, the pavement structure on top of the earthen fill is shifted. The shifting of the pavement structure results in damage to the pavement structure, which can shorten the life cycle of the pavement structure.
The use of rigid foam to provide a stable roadbed over an unstable soil material is known in the art. The foam is typically used in the form of blocks. The foam blocks are placed in layers to form the desired road bed configuration. As the foam blocks are laid, timber fasteners are positioned at regular intervals to retain the foam blocks in the desired configuration until a pavement structure is formed on the foam block structure. The timber fasteners are formed from metallic materials, such as malleable iron, and have a plurality of outwardly extending spikes.
The use of foam as a base over unstable soil is described in Monahan, U.S. Pat. No. 3,626,702 (the "Monahan '702 patent"). The Monahan '702 patent indicates that polyurethane foam can provide a base beneath a road or building foundation.
Rigid polyurethane foam has also been used as retaining wall backfill as described in Monahan, U.S. Pat. No. 3,747,353 (the "Monahan '353 patent"). The Monahan '353 patent indicates that the foam reduces pressure on the retaining wall. The polyurethane foam is either cast at the site or formed elsewhere and delivered to the site in slabs. The Monahan '353 patent also discloses that a pavement surface may be formed on the backfill material to provide a level roadway in regions where the terrain is sloped.
None of the prior art references describe using foam block backfill in conjunction with bridge abutments and bridges or in conjunction with constructing buildings on rock surfaces. Accordingly, the references do not appreciate the advantages that foam blocks provide when used to backfill a structure such as a bridge abutment or a dwelling. Furthermore, none of the references disclose using foam block backfill in conjunction with alternative abutment designs, which are made possible because of the reduced horizontal pressure that the foam block backfill exerts on the abutment.